Coronary artery disease (CAD) is characterized by a narrowing of a section of the coronary artery tree, which supplies blood to the heart. The narrowing is caused by atherosclerotic plaques, which impair blood flow through the arteries. The lack of blood flow to the heart, caused by this condition, can eventually result in a myocardial infarction, or heart attack. Over 13 million people in the US have CAD. It is the leading cause of death in the US, claiming over 1.4 million lives each year. Approximately 6 million patients arrive in US hospital emergency rooms annually with chest pain. The hospital staff need to quickly determine whether a patient is suffering from a CAD induced attack. A diagnostic coronary angiogram is used to determine whether or not to perform surgery (coronary bypass), or an interventional procedure (e.g., insertion of a stent), to open a narrowed artery. Methods for creating a diagnostic image of the coronary arteries include, use of two-dimensional X-ray angiography and three-dimensional CT angiography. The determination of “diagnostic quality” in an image is achieved by being able to identify coronary lesions (narrowings) with a high degree of sensitivity and specificity.
In 2D X-ray angiography, a patient needs to have a catheter inserted into an artery near the groin. The catheter is navigated through the arterial system to the ostium of a coronary artery, under the guidance of an X-ray angiography system. A contrast agent is injected directly into the coronary artery, via the catheter, while the X-ray angiography system records a rapid (˜30 fps) sequence of images of the opacified artery tree. This two-dimensional image sequence (or Cine angiogram) normally includes the entire artery tree. Cine angiograms are often taken at other X-ray tube-detector angulations to acquire additional views of the artery tree, to help overcome limitations inherent in using a two-dimensional image to examine a three dimensional object.
Coronary angiography suffers from several limitations. The X-ray systems used are relatively expensive. Access to a patient arterial system (to place the catheter) is required (increasing the risk of complication), and known typical contrast agents can further harm compromised kidneys, in some cases resulting in kidney failure. Further, a procedure requires a physician (interventional cardiologist) and other staff members (two or more) to gain arterial access, run the angiography system and care for a patient. Intra-procedure 3D imaging (i.e. that is performed during an interventional procedure, rather than before or after the interventional procedure) uses C-arm CT (computed tomography), whereby a C-arm of the angiography system (which contains both the X-ray tube and detector), rotates around the patient while capturing a series of images at closely spaced angulations. The acquired images are used to create a three-dimensional image of patient anatomy (including vessels, if contrast agent is injected). A limitation in use of C-arm CT is temporal resolution. (1 rotation per 5 seconds) Methods to image coronary arteries with C-arm CT include use of multiple rotations with retrospective cardiac gating as well as use of a single C-arm rotation, together with a motion compensation process in image reconstruction. These known methods fail to provide diagnostic image quality.
Computed Tomography (CT) Angiography enables capture of coronary images of diagnostic quality using scanners that rotate at high speeds and with high numbers of radiation detector rows (up to 320, which increases the amount of anatomy that can be imaged in a single rotation). CT systems capable of diagnostic image quality are expensive and CT has the same risks in use of contrast agent as angiography systems. CT also may lack reliability in capturing images during administration of a bolus of contrast agent as it moves through coronary arteries and an image may need to be captured during a single phase of a cardiac cycle in a window of several milliseconds. Further, both Angiography and CT use radio-opaque (iodinated) contrast agent to illuminate vessels for X-ray imaging. This agent is usually delivered as a bolus and is cleared rapidly by the kidneys, such that the only opportunity to image the area-of-interest is during a “first pass” of contrast agent through that area. Furthermore, since the contrast bolus moving through the vessels is a dynamic event, the time (relative to the start of contrast injection) when the image needs to be acquired is not always predictable, and the contrast agent does not always completely mix with the blood, and can cause artifacts in acquired X-ray images (both 2D and 3D). The limitations of iodinated contrast agents have resulted in the development of sophisticated and expensive imaging systems, for both angiography and CT, which are designed to capture images quickly, as the contrast agent rapidly moves through the blood vessels to be imaged. These systems are required to be fast because of the short life of contrast agent in the vessels, and the motion of the beating heart. A system according to invention principles addresses these deficiencies and related problems